Vacuum deposition is a common method for coating metals such as aluminum, copper, zinc, and tin onto various substrates of metal, glass and plastic. The metal is vaporized in a vessel commonly referred to as a "vaporization boat" by electric resistance heating. The vessel is connected to a source of electrical power to heat the vessel to a temperature which will cause the metal charge in contact with the boat to vaporize. Typically, the product is placed in an evacuated chamber within which the metal is vaporized. The product may be fed individually or continuously into the chamber or, alternatively, may form part of the chamber itself. A wide variety of product is coated with metal using vapor deposition including, e.g., television picture tubes, automobile headlights, toys and the like.
The metal charge is placed in a cavity recess machined into the top surface of the vessel. Upon reaching the vaporization temperature of the metal the metal charge melts and quickly vaporizes. The charge flashes in a vigorous and abrupt manner and the process is repeated with a new charge of metal. The number of flashes which can be performed in a given time period controls product production. Accordingly, the number of flashes a vessel can sustain without failure is a critical performance characteristic of the process. Conversely, when failure occurs the parts being coated are scrapped or have to be redone which involves additional time and cost. To avoid this extra cost the vaporization vessel may be discarded before anticipated failure. A vaporization vessel with a short lifetime increases the production cost per part and reduces efficiency.